Field Drying Forage for Hay and Haylage
by Dan Undersander and Craig Saxe
How does forage dry?
If we understand and use the biology and physics of
forage drying, not only does the hay or haylage dry
faster and have less chance of being rained on, but the
total digestible nutrients (TDN) of the harvested forage
are higher. As mowing and conditioning equipment has
evolved, some of the basic drying principles of forage
have slipped by the wayside and we need to review
them.
The first phase of drying is moisture loss from the
leaves through the stomata. Stomata are the openings
in the leaf surface that allow moisture evaporation from
the plant to cool it and carbon dioxide uptake from the air
as the plant is growing. Stomata open in daylight and
close when in dark and when moisture stress is severe.
Cut forage laid in a wide swath maximizes the amount of
forage exposed to sunlight. This keeps more stomata
open and encourages rapid drying which is crucial at this
stage because plant respiration continues after the plant
is cut. Respiration rate is highest at cutting and
gradually declines until plant moisture content has fallen
below 60%. Therefore rapid initial drying to lose the first
15% moisture will reduce loss of starches and sugars
and preserve more total digestible nutrients in the
harvested forage. This initial moisture loss is not affected
by conditioning.
The second phase of drying is moisture loss from
both the leaf surface (stomata have closed) and from the
stem. At this stage conditioning can help increase drying
rate, especially as the forage becomes drier.
The final phase of drying is the loss of tightly held
water, particularly from the stems. Conditioning is critical
to enhance drying during this phase. Conditioning to
break stems every two inches or scrape the waxy cuticle
off will increase water loss through the waxy cuticle of
the stem.
Dan Undersander, Extension Forage Agronomist
[email protected]
Craig Saxe, Juneau County UW-Extension
[email protected]
How does swath width influence drying rate?
Understanding these principles will allow us to
develop management practices in the field that maximize
drying rate and TON of the harvested forage. The first
concept is that a wide swath immediately after
cutting is the single most important factor maximizing
initial drying rate and preserving of starches and sugars.
In a trial at the UW Arlington Research Station (Figure 2)
where alfalfa was put into a wide swath (covering >70%
of cut area) it reached 65% moisture in about 8 hours
and could be harvested for haylage the same day as
cutting. The same forage from the same fields put into a
narrow windrow (covering approximately 30% of cut
area) was not ready to be harvested until late in the day
or the next day!
In fact, a wide swath may be more important than
conditioning for haylage.
The importance of a wide swath is supported from
drying measurements taken at the Wisconsin Farm
Technology Days in 2002 (figure 3) where different
Figure 2. Effect of wide swath vs narrow swath drying rate,
Arlington WI, July 2007
90
80
wide swath
narrow swath
70
Percent Moisture
The general pattern of drying forages is shown in the
figure at right. When forage is cut, it has 75 to 80
percent moisture that must be dried down to 60 to 65%
moisture content for haylage and down to 14 to 18%
moisture content for hay (lower figures for larger bales).
60
50
40
30
20
10
0
5
8
24
29
32
48
53
56
Hours After Cutting
Focus on Forage - Vol 12: No. 5 (Updated 04/2013)
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mower-conditioners mowed and conditioned strips of
alfalfa and put the cut forage in windrow widths of the
operators choice. Moisture content of the alfalfa was
measured 5.5 hours after mowing. Each point is a
different machine that included sickle bar and disc
mowers and conditioners with steel, rubber or combination rollers. Across all mower types and designs, the
most significant factor in drying rate was the width of the
windrow.
In figure 3, note the one outlying point at 70%
moisture content and a windrow width/cut width ratio of
0.48. This shows how much drying can be slowed by
improper adjustment of the conditioner.
Figure 3. Moisture content of alfalfa 5.5 hours after cutting with
various windrow width to cut width ratios, WI Farm Technology
Days, 2002
75
y = -11.93ln(x) + 44.2
R² = 0.33
Moisture content (%)
70
65
60
55
50
45
40
0.00
0.20
0.40
0.60
0.80
Windrow width/cut width
Many farmers have gradually gone to making
windrows that are smaller percentages of the cut area as
mowers have increased in size. Generally, the
conditioner has stayed the same size as mower cutting
bars have gotten bigger, resulting in narrower windrows.
There is some variation among makes and models and
growers should look for those machines that make the
widest swath.
Does swath width influence forage quality?
Putting alfalfa into wide swaths (72% of cut width)
immediately after cutting often results in improved quality
of alfalfa haylage compared to narrow windrows (25% of
cut width) in studies at UW Arlington and Marshfield
Research Stations in 2005 to 2007 (Table 1 ). Alfalfa
was mowed with a discbine, conditioned, and haylage
was sampled approximately two months after ensiling in
tubes. The alfalfa from the wide swaths had 1.0% less
NDF, and 1.7% more NFC. Haylage from the wide
swath had more substrate for fermentation which
resulted in more lactic and acetic acid. The higher acid
content would indicate less rapid spoilage on feedout.
A wide swath requires that one or both tractor
wheels drive over the swath. While this may not be
desirable, it results in less loss than making a narrow
windrow. The reduced drying of the wide swath with a
driven-over portion is less than if a narrow windrow is
Focus on Forage - Vol 12: No. 5 (Updated 04/2013)
Table 1. Difference in composition of alfalfa haylage
made from narrow and wide swaths after ensiling, 8
trials - Arlington & Marshfield, 2005-2007
Factor
Hours to dry to 65% moisture
Wide – Narrow Swath
Difference
-10.8
Crude Protein, %
0.5
NDF, %
-1.0
NFC, %
1.7
Ash, %
-0.2
Lactic acid, %
0.8
Acetic Acid, %
-0.2
Relative Forage Quality
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made. Also, as table 1 shows, the ash content of
haylage from wide swath alfalfa was actually less than
from narrow windrows with no wheel track. Narrow
windrows tend to settle to the ground causing soil to be
included with the bottom of the windrow when it is picked
up. Wide swaths tend to lay on top of the cut stubble
staying off the ground. Driving on the swath can be
minimized by driving one wheel on the area between
swaths if swath covers less than the full cut width.
Grasses, especially if no stems are present, must be
laid into a wide swath when cut. They generally must
also be tedded about 24 hours after cutting and then
raked into a windrow later. Grass forage, when put into
a windrow at cutting, will settle together, dry very slowly
and be difficult to loosen up to increase drying rate.
Recommendations
1. Cut at the proper height – 2 to 4 inches for alfalfa and 3
to 4 inches for grass or legume/grass mixtures.
2. Adjust conditioner properly. Roller conditioners are best
for alfalfa due to reduced leaf loss. Either type, if
properly adjusted (1 to 5% of leaves show some bruising),
will cause drying at a similar rate.
3. Lay hay in a wide swath covering 70% or more of the
cut area to enhance rapid initial drying.
4. Rake/merge ahead of chopping or at a moisture content
that minimizes leaf loss for hay (40 to 60% moisture –
often reached 24 hours after mowing).
For more information see Best Practices to Hasten Field
Drying of Grasses and Alfalfa, UWEX A3927, available
from University of Wisconsin at: http://learningstore.uwex.edu/.
 University of Wisconsin Board of Regents, 2013
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